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As Autumn begins and the nights lengthen, explore the heavens with the aid of:

The Australian Night Sky - March 2017

By Wayne Roberts

What's In The Sky This Month

The Planets

Our Monthly Feature

 

[Click here to show or hide the explanatory notes]
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What's in the sky this month; March 2017:

 2nd Neptune in conjunction with the Sun.
 3rd Venus stationary;
     Moon at perigee (closest to Earth, 369,062 km).
 5th Aldebaran (Alpha [α] Tauri) occulted by Moon (not from Australia, see below);
     First Quarter Moon.
 7th Asteroid 4Vesta (featured in last month’s ANS) stationary (ends retrograde motion);
     Mercury in superior conjunction (on the opposite side of the Sun to Earth).
10th Comet Encke at perihelion (see below).
11th Regulus (Alpha Leonis) occulted by Moon (not from Australia, see below).
13th Full Moon.
15th Gamma Normid meteor shower peaks (see below).
18th Saturn at western quadrature (see planetary notes to follow).
19th Moon at apogee (farthest from Earth, 404,650 km).
20th Earth at March equinox (see planetary section below).
21st Last Quarter Moon.
24th Mercury at perihelion (closest to Sun, 46.00 million km/0.3075 au).
25th Venus in inferior conjunction (passing between Earth and the Sun).
26th Neptune occulted by Moon (not from Australia, see below).
28th New Moon.
30th Moon at perigee, 363,854 Km.

N.B.: When reading the following, refer back to the explanatory notes at the beginning of this article (click on the above link to expand) for information on terminology, angular separation approximations and adjustment of latitude & longitude.

Note also that the occurrences of aphelion and perihelion shown above relate to the physical separation of the Sun and the relevant planet, and are unrelated to their angular separation in our sky.

Unfortunately, none of the occultations by the Moon this month – of Aldebaran on the 5th, Regulus on the 11th and Neptune on the 26th – are visible from Australia; all, in fact, are merely close conjunctions from our perspective, and are further devalued courtesy of closest approach occurring, in each case, when the respective pairs are below our horizon.

The Solomon Islands, Micronesia, Hawaii and Central America are favoured for the Aldebaran event; for us, the 46% first quarter Moon’s limb passes 24' [" denotes arc-second = 1/60th of an arc-minute (symbol ') or 1/3600th of a degree (symbol °)] from the star at 12:28 pm, 17° below our eastern horizon. Regulus’ occultation can be seen from southern South America and far south South Africa; locally, closest approach of the limb of the 97% waxing gibbous Moon to the planet is 12', and occurs at 10:15 am, 53° below the SW horizon. The Neptune occultation can be viewed by those in South Africa, SW Asia, Yemen and Oman, but the 4% illuminated waning crescent Moon never approaches closer to the planet than just over ½° from our viewpoint, and does so 20° below the horizon in the WSW, at 8:10 pm.

Comet 2P/Encke was the 2nd comet (after Halley’s comet) recognised to return periodically, as its designation implies; it has a very short period of 3.3 years, the shortest of all relatively bright comets. Encke reaches perihelion, its closest point to the Sun, at 1:15 pm on the 10th, at a distance of 0.336 au/50.3 million km, but is unobservable at this time, setting just over 10 minutes after sunset. Its closest point to Earth is reached at 5:16 pm two days later, 0.655 au/98.0 million km away; on this day of the 12th it has transitioned, albeit in name only, to our morning skies, rising only 5 minutes before the Sun and being less than 1° above the horizon at sunrise.

Encke will by no means be a visual spectacle, but its earlier rising and consequent increasing distance from the Sun in an ever darker sky, should render it visible in a finder ‘scope or binoculars in the days either side of the 20th, when its dwindling brightness is expected to remain at around at 6th magnitude. The following chart is configured for 6:23 am on the 20th, one hour before sunrise (7:23 am), with the comet at an altitude of 9½° (about the span of a fist at arm’s length). The chart includes a marker – a green cross – for the comet’s position at the end of the month, at 6:33 am, again an hour before sunrise (7:33 am). Note that the horizon at 7:33 am on the 31st will be lower than where it appears on the chart by almost exactly twice the distance between the comet’s two plotted positions. The relatively bright star Fomalhaut (Alpha Piscis Austrini, mag 1.2) is also plotted as a reference point.

In choosing a date for targeting the comet through binoculars or a ‘scope, bear in mind that the Moon will be fully illuminated low in the west in the early morning of the 12th, and will subsequently move eastwards and decrease in phase with each passing day. It will sit high in the sky on the morning of the 20th, 58% illuminated and therefore still significantly affecting views of the comet. On the morning of the 25th, our satellite will be 13% illuminated, sitting 14° to the upper left (west) of Encke; the following morning it will be 8° to the comet’s lower left (NE), and a scant 6% illuminated. Your viewing activities must therefore walk a tightrope, balancing the decreasing impact of the Moon against the intrinsically reducing visual magnitude of the comet – I would tentatively suggest views from the 25th onwards.

Only one meteor shower, the Gamma Normids, peaks this month, on the 15th; unfortunately it is not one known for prolific activity, having a modest ZHR of six. As the radiant of this shower is very nearly circumpolar, it’s a pity that the 96% illuminated waning gibbous Moon rises at 8:44 pm (on the 14th) and is up all night, heavily degrading whatever action may be on offer.

Having risen at 7:15 pm on the 14th, the radiant then transits at 6:27 am; if you’re an avid meteor shower fan and/or plan to be up early on the morning of the 15th, you may use the following chart, configured for 3:00 am, to show you where the radiant is positioned. The boundary of the circumpolar region is plotted – all stars within the red circle orbit around the SCP without ever dipping below the horizon.

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THE PLANETS

Mercury

March 2017 and Mercury are a bad combination for those in the southern hemisphere. The innermost planet begins the month deep in twilight, in the last week of a morning apparition. Swinging around the far side of the Sun from our perspective, referred to as being in superior conjunction, on the 7th, the planet then emerges into our evening skies, beginning its poorest such apparition for the year, remaining deep within evening twilight throughout.

For the record, its relevant statistics for the 1st, the 25th (which we’ll adopt as our viewing night, being a Saturday preceding the New Moon of the 28th) and the 31st are respectively: rise 6:36 am, 5° clear of the eastern horizon when the Sun rises at 7:04 am, disk span 4.9", 99% illuminated and shining at magnitude -1.2; just over 6° high at 7:24 pm sunset, set 7:58 pm, disk 6.3", phase 69%, magnitude -0.9; and finally altitude less than 6¼° when the Sun sets at 7:15 pm, set 7:51 pm, disk 7.3", phase 46%, magnitude -0.2.

As the above figures show, the planet is intrinsically quite bright, both when in the morning sky early in the month and the evening sky later, but is in close proximity to the Sun throughout and swamped by twilight. Save your dates with Mercury for its next two apparitions, each the best of the year in their respective time slots, May-June in the morning sky and July-August in the evening.

Beginning the month in Aquarius, the Messenger of the Gods crosses the border into Pisces on the 11th, zips across a corner of Cetus (a constellation which is not part of the zodiacal group that the planets traditionally ply) between 1:21 am and 4:01 am on the 18th, before returning to Pisces, then finishes the month just 1½ hours short of transitioning into Aries.

Venus

After ruling the western sky in the evenings since last July, Venus finally succumbs to the horizon this month, swinging in between Earth and the Sun (when it is said to be in inferior conjunction) on the 25th. Being so close to conjunction would rule out views of any other planet, but brilliant Venus defies this trend and actually offers spectacular telescopic views early in the month as its disk swells past a huge 50" (even mighty Jupiter never exceeds 50.1" at its very best), as a beautiful thin crescent.

As March begins, Venus is deep within twilight, but its sheer brilliance punches through the Sun’s residual glow. It sets just over ¾ hour after the Sun, 8:48 pm vs 8:00 , having been a mere 8½° above the western horizon at sunset. Nevertheless, barring cloud or excessive pollutants (referred to as ‘poor transparency’), and with an unobstructed western horizon, truly memorable telescopic views are to be had of its 47" disk, just 17% illuminated and shining at a scintillating magnitude -4.6. Two days later on the 3rd, it is said to be stationary as it ceases to move eastwards relative to the stars and begins to loop around and accelerate towards the western horizon.

Venus quickly descends to the horizon and is too low to view after a week and a half or so; it is obviously disqualified as a target on our viewing night of the 25th, being in inferior conjunction. Just six days later on the 31st, you may wish to try your luck spotting it low in the morning sky before sunup – a ludicrous prospect for any other planet, but one which, if successful, will place a truly humungous 58" disk in the eyepiece, as a razor thin 2% crescent shining at magnitude -4.1. Because the planet doesn’t rise until 7:02 am, barely over half an hour before the Sun rises at 7:33 pm, take extreme care not to allow the Sun to enter the field of view of your optics, less instant and irreparable eye damage results. Venus remains within Pisces throughout March, apart from clipping a corner of Pegasus between 12:29 pm and 3:24 pm on the 29th (another brief planetary excursion into a non-zodiacal constellation, ala Mercury’s effort earlier in the month).

Earth

Our home planet gets a mention this month, reaching the autumnal equinox (spring equinox in the northern hemisphere) on the 20th, with the Sun rising due east and setting due west, day and night being of approximately equal length. Approximately is the operative word here, as the date when day and night are most nearly of equal length at a given location is dependent on its latitude. The March equinox – which signals the time when the Sun crosses the celestial equator, the projection into space of our earthly equator, from south to north – always occurs on the 19th, 20th or 21st; however, the date when the length of day and night most closely coincide varies by as much as several weeks if regions close to the equator are included in consideration. Here’s a chart from www.timeanddate.com illustrating the variation for both the March and September equinox:

As the chart indicates, day and night are closest to being of equal length on the 23rd/24th at the location for which these viewing notes are configured, Melbourne Observatory, latitude 37°50' – Starry Night software indicates sunset on the 23rd at 7:27:18 pm, and sunrise and sunset on the 24th at 7:26:30 am & 7:25:46 pm respectively, whereby the daylight hours of the 24th exceed those of the night of the 23rd/24th by all of four seconds.

Interestingly, the chart states that day and night are not of equal length on the equator, which you may find counter intuitive. Selecting a few sites on the equator at random and checking their sunrise and sunset times confirms that daylight always exceeds night by about seven minutes – why is this so? (Check the internet or drop me a line at the address at the end of these viewing notes if you can’t come to grips with this).

Mars

Mars continues its leisurely stroll towards the horizon; it has lingered in the west for months and will do so for a few months to come, not dipping below the sunset horizon until late July. March will be its last full month clear of evening twilight, as it will begin setting in twilight early next month (on the 5th).

On March 1st, Mars is at an altitude of 19° at sunset and sets just shy of 1¾ hours after the Sun, 9:44 pm as against 8:00 pm. Its increasing distance from Earth causes its 94% illuminated disk to appear very small, spanning just 4.6"; it is still fairly conspicuous thanks to its ruddy glow and relative brightness in a portion of sky lacking stars bright enough to rival it, shining at magnitude 1.30.

Come our viewing night of the 25th, setting time is in to 8:55 pm, now just over 1½ hours after sunset (7:24 pm), when it stood 16° above the horizon; the disk now shows a 96% phase, spans 4.3" and shines at magnitude 1.43. Here’s where it sits, at an altitude of just 5¼°, at 8:24 pm, one hour after sunset. Expect to see no detail on the Martian disk; it’s far too small.

By the end of the month, Mars’ circumstances have further deteriorated, albeit slightly: it sets just under 1½ hours after the Sun – 8:44 pm vs 7:15 pm – and is 15° above the sunset horizon; the span of its disk is down to 4.2", still 96% illuminated, and brightness has decreased marginally to magnitude 1.46.

The Red Planet transitions from Pisces into Aries, where it sees out the month, on the 9th.

Jupiter

The King of the Planets is now well established in our evening skies, rising before the cessation of evening twilight after the first week of March. On the 1st, the King rises at 9:41 pm, just ten minutes after the sky fully darkens, and transits at 4:06 am (on the morning of the 2nd); its 42.2" disk shines at magnitude -2.33.

By the 25th, only two weeks short of opposition, the planet is becoming ever more viewer friendly, rising at 8:01 pm, well over ¾ hour before twilight finishes, and subsequently transiting at 2:23 am; span and brightness have also improved, to 43.9" and magnitude -2.44. Jupiter itself is easy to identify as, with Venus out of the picture, it is by far the brightest point of light in the sky. Here’s a magnified view of Jupiter and its four Galilean Moons at 11pm, with the planet having attained an altitude of 34° in the ENE.

All four moons – Europa, magnitude 5.5, Io, mag 5.3, Ganymede, mag 4.85 and Callisto, mag 5.9 – are moving away from Jupiter, Europa to the east and the other three to the west; Callisto is nearing its greatest angular separation west. No stars in the field covered by the chart can be mistaken for the Jovian moons – the star just to Jupiter’s lower left, TYC4964-597-1 is brighter by far than any other, and shines faintly, at magnitude 11.5.

At month’s end, Jupiter’s rise time has further improved, to 7:36 pm, and it’s 13° clear of the horizon when twilight fades at 8:43 pm; the span of its disk has improved a touch, to 44.1", as has its brightness, to magnitude -2.45.

Jupiter will remain within the constellation of Virgo until November.

Saturn

Saturn and its beautiful ring system begin their transition from morning to evening skies this month, rising before midnight on and after the 20th (it actually rises twice on the 20th – at 12:04 am, just after midnight, and again just under 24 hours later, at 11:59:50 pm, mere seconds before the calendar clicks over to the 21st). As March begins, the Ringed Wonder rises at 1:15 am. Its disk spans 16.2", the visually stunning ring system 36.7" at an inclination of 26.54°; disk and rings together shine at magnitude 0.51.

Saturn is at western quadrature on the 18th, when the Sun-Earth-Saturn angle is 90°, as shown in the following depiction taken from the excellent publication Astronomy Australia 2017; it is at this time that Saturn’s disk throws its greatest shadow on the back of the ring system.

This illustration, variations of which are often carried on astronomical sites and publications, can be misleading to the uninitiated. To interpret it correctly, first of all appreciate that the diagram shows the solar system from a point in space north of the Sun, and that all the planets revolve in an anticlockwise direction from this perspective.

Therefore, the inner planets, which zip around faster than us, are moving anticlockwise in relation to Earth, but we are leaving the slower outer planets behind as we orbit, so they are effectively moving clockwise in relation to us.

Consequently, the order of events shown on the diagram for the inner planets should be read anticlockwise, but those for the outer planets clockwise. Thus Venus and Mercury are at greatest eastern elongation, then inferior conjunction, then greatest western elongation, then superior conjunction, while the outer planets are at western quadrature, then opposition, then eastern quadrature, then conjunction.

On our designated viewing night of the 25th, Saturn breaches the eastern horizon at 11:41 pm; the span of the disk is out to 16.8", and that of the rings to 38.2". The inclination of the ring system, nearing the end of a short term closing trend (which ends half way through next month before resuming the current long term opening trend towards their maximum, just shy of 27°, in October), has reduced to 26.45°; the planet has brightened a little to magnitude 0.44. The chart below shows where the planet sits at an altitude of 37° in the eastern sky, at 3:00 am on the morning of the 26th, in relation to star patterns in Sagittarius and Scorpius. As it is noticeably brighter than even the brightest star shown, Antares (Alpha Scorpii, mag 1.0), identification should not be difficult.

The magnification to follow shows five of Saturn’s seven brightest moons; their visual magnitudes, taken from Starry Night software, are as follows: Rhea 10.1, Tethys 10.6, Mimas 13.3, Dione 10.8 and Enceladus 12.1. The USNO designated star, magnitude 14.9, is the brightest star in the field; as it shines 1½ magnitudes fainter than even tiny dim Mimas, and will go undetected in other than large ‘scopes, it serves to illustrate that no stars can be mistaken for moons.

This final chart zooms out a little to take in the outlying Titan and Iapetus, which shine at magnitudes 8.7 and 11.6 respectively. Titan’s brightness rating is also from Starry Night; Iapetus’ which has one hemisphere much brighter than the others – a very significant fact which the software unfortunately doesn’t take into account – is my own confident estimate, based on a relatively simple calculation. As was the case with the previous chart, all stars will probably remain unseen and, in any case, are far too faint to be mistaken for the moons. With this in mind, both moons, especially bright Titan, should stand out and be easily identified by looking in the direction and at the distance shown from Saturn; the more so because they form a near straight line with their parent body.

Titan will be visible through any telescope (and probably faintly visible through a finder ‘scope or binoculars); a six inch ‘scope should reel in Rhea, Tethys, Dione and perhaps Iapetus; Enceladus (and Iapetus?) may call for an eight to ten incher; while a twelve incher might be required to bag Mimas.

On the 31st, Saturn is rising at 11:17 pm; its disk spans 17.0", the ring system more than double that, at 38.5", inclined at a marginally reduced 26.44°. The combined visual magnitude of disk and rings has improved to 0.41.

Saturn will remain within Sagittarius until May 19th, when it backtracks temporarily into Ophiuchus, under the action of retrograde motion.

Uranus

The ice giant Uranus, the second outermost planet proper since Pluto’s demotion to the status of dwarf planet, has all but run its race this time around, reaching conjunction with the Sun on the 14th of next month. At the beginning of March, Uranus is setting at 9:43 pm, just under 1¾ hours after the Sun (8:00 pm), and a scant twelve minutes after evening twilight subsides.

On the 25th, it’s very poorly positioned, setting at 8:11 pm, just a little over ¾ hour after the 7:24 pm sunset, and a little under ¾ hour before twilight wraps up at 8:52 pm. On March 31st, these data read 7:49 pm, just over ½ hour, 7:15 pm, approaching one hour before, and 8:43 pm. Uranus’ disk spans 3.4" throughout the month, its visual magnitude reducing by an inconsequential amount, from magnitude 5.88 to 5.91.

The chart below, configured for sunset (7:24 pm) on our viewing night of the 25th, illustrates how poorly Uranus is positioned, sitting a mere 8½° above the horizon, well below Mars and in the company of Mercury, which is even more poorly positioned, albeit shining much more vigorously.

The planet will remain within the constellation of Pisces until 2018/19.

Neptune

Viewing prospects for Neptune are even less inviting, as it is in conjunction with the Sun this month, on the 2nd. Even the fact that the ecliptic – the path across the sky followed by the Sun and, very nearly, the planets – rises very steeply away from the horizon on March mornings cannot elevate Neptune to an altitude clear of morning twilight. For the record, Neptune’s rise time & altitude at sunrise, and the time of sunrise, for the 1st, 25th and 31st, are respectively: 7:11 am & -2° (rises after 7:04 am sunrise); 5:41 am & 21° @ 7:27; 5:18 am & 26° @ 7:33 am. The planet’s disk spans 2.2" throughout March, and brightens imperceptibly from magnitude 7.96 to 7.95 from the start to the finish of the month.

The giant ball of gas, liquid and ices (with a rocky core) will be in Aquarius until 2022/23.

Pluto

Pluto is now high in the sky in the pre-dawn hours, but in keeping with past practice, detailed finder charts will not be provided here until the months around and following opposition, which occurs in July; the rationale is that the tiny frozen orb, swimming through the heavily populated star fields of Sagittarius, is best targeted when near its maximum altitude for the evening at a viewer friendly hour. With this in mind, these viewing notes will continue to give its general location up until June, when an intermediate level of resolution will be introduced, with fully detailed finder charts joining the fray in July and for a few months following.

On the first day of March, Pluto doesn’t breach the eastern horizon until 2:53 am, and has attained an altitude of 30° at the beginning of morning twilight, 5:32 am. By the 25th, rise time is in to 1:21 am, and the planet (in defiance of the boffins at the IAU) is 53° clear of the horizon when the sky begins to brighten at 6:00 am (still well short of its transit [8:33 am] altitude of 73°); at month’s end, these figures read 12:57 am, 58°, 6:05 am, 8:09 am and 73°.

Here’s an indication of its location at 5:00 am on the morning of the 26th, near the three naked eye stars below the handle of the teapot asterism (above the handle actually, the teapot sits upside down from our viewing perspective). The visual magnitudes of the labelled stars are: Albaldah (Pi [π] Sagittarii), 2.9; Omicron [ο] Sag, 3.75; Xi22] Sag, 3.5; Saturn, mag 0.4, is also labelled as an aid in orientation. The faintest stars shown are around magnitude 6.0, a little fainter than visible to the naked eye for most folk, under other than the darkest of skies.

Pluto will reside within Sagittarius until 2023 (for January and February and early July onwards, with the intervening months spent in neighbouring Capricornus), and the first few days of 2024.

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Our Monthly Feature

Our feature article this month is the Rosette Nebula, so named because of its circular red appearance when viewed through very powerful telescopes. The Rosette is a star forming region and an emission nebula which glows because atoms within the gas clouds of the nebula are excited by radiation from the stars which have formed from its material; it sits some 5000 light years away and spans more than 50 light years.

The Rosette is collectively described by the NGC designations 2237, 2238, 2239 and 2246; all these nebula were separately discovered in the 18th and 19th centuries, before the light gathering power of modern observatory class telescopes made it clear that they are part of a whole.

At the centre of the Rosette is the open star cluster NGC 2244, which was first discovered by the English astronomer John Flamsteed in 1690; the radiation from the cluster has blown away much of the gas and dust at the nebula’s centre. The fact that Flamsteed did not see the nebula, along with the initial identification of multiple nebulae thought to be independent of each other (the four NGC designations listed above), is testimony to the nebula’s faintness (there is an even fainter and larger extension of the nebulosity to the left hand side of the image further down in this article).

Through amateur instruments, the nebula is very faint – the red colour seen by larger instruments is hinted at by the Rosette’s dark appearance (in stark contrast to the predominantly brighter appearance of the well known Orion Nebula). The Rosette itself is very difficult to spot, only extremely faintly visible through binoculars or a finder ‘scope, and then only knowing where to look and using averted vision. Fortunately, the afore-mentioned central cluster, NGC 2244, is easily visible in a finder, appearing as two parallel lines of, principally, three stars each; the cluster is even visible to the naked eye, under dark skies, as a very faint ‘star’.

The following chart, configured for 8:52 pm on the 25th, just as twilight is fully extinguished, will facilitate identification of the cluster and hence the nebula; this early time is chosen because the Rosette is already past its highest altitude of the evening as all light fades. The text below the chart indicates the best way to identify the cluster which betrays the nebula’s location:

All star charts courtesy of StarryNight®ProTM Version 7.5.5.1109/Simulation Curriculum Corp.

Begin by identifying the prominent constellation of Orion in the NW sky. Now turn your attention towards Bellatrix (Gamma [γ] Orionis), magnitude 1.6 and Betelgeuse (Alpha Orionis), magnitude 0.4. Construct, in your mind’s eye, a line from Bellatrix to Betelgeuse, then veer left 30° and continue a similar distance to the faint, but still naked eye (under other than light polluted skies) star 8 Monocerotis, magnitude 4.4. From 8 Mon, turn right, as shown in the chart, at an angle of around 75°, not quite a right angle; a touch under half the Betelgeuse-8 Mon distance away, you’ll see a star of similar brightness (to 8 Mon), 13 Mon, magnitude 4.5. As the chart shows, the nebula forms the apex of a triangle with baseline 8 Mon to 13 Mon, a little closer to the former – if you look closely at the location indicated, you will see, providing your sky is dark, an even fainter ‘star’, which is in fact NGC 2244, the cluster within the nebula.

Targeting this spot through your finder scope, you’ll see the cluster as the two (quite small at this resolution) parallel lines of stars mentioned earlier. Centre the cluster then examine it through the main eyepiece at low power. The nebula surrounds the cluster, but because of its faintness, you probably won’t detect it in all directions – through my twelve inch reflector, I see a very faint dark cloud in some directions but not others. While the eye’s sensitivity in insufficient to show the red colour, it is, with the benefit of foreknowledge, easy to picture the dark murky nebula as red.

Experimenting with various filters, I found the appearance of the nebula slightly enhanced by a wide bandwidth filter – referred to as a deep sky filter – and perhaps just a little better again through a narrow band OIII (Oxygen three) filter.

Here’s an image of the nebula taken by the Palomar Observatory in San Diego, California; the cluster and the region of gas and dust cleared by the radiation from its stars, are prominently visible in the centre.

As always, any questions, comments or suggestions are welcome and may be directed to: waynerobertsau@yahoo.com.au

Until next month:

CLEAR SKIES and HAPPY HUNTING